In the field of cooling and heating, chlorinated hydrocarbons (chlorofluorocarbon, CFC) such as R11 (trichlorofluoromethane) and R12 (dichlorodifluoromethane) have been largely eliminated due to their adverse impact on the earth's ozone layer. Chlorinated fluorocarbons were initially replaced with hydrochlorofluorocarbons such as R22 (chlorodifluoromethane); however, continued concerns with their ozone depleting potential (ODP) and new concerns with the compounds' global warming potential (GWP) has led to their replacement with fluorinated hydrocarbons like R134a (1,1,1,2-tetrafluoroethane) or R32 (difluoromethane). Currently, R134a is used widely in both stationary and mobile refrigeration systems. Continued concerns with GWP, coupled with performance requirements in vapor compression heat transfer systems, have led to the development of new refrigerants such as fluorinated unsaturated hydrocarbons (i.e., fluorinated olefins) like trans-1,333-tetrafluoropropene (R1234ze).
Although chlorine-containing refrigerants have been discontinued by the mainstream refrigeration supply industry, they continue to be available through alternative distribution channels. Some of these compounds are used legitimately in applications such as chemical manufacturing and processing, laboratory use, and other non-refrigerant applications, or for limited use in older HVAC and refrigeration systems that are not compatible with newer refrigerants, they are also used illegitimately as a substitute for non-chlorinated refrigerants in systems that are designed for non-chlorinated refrigerants. Counterfeit refrigerants containing varying amount of ozone-depleting chlorinated substances make them illegal in certain parts of the world under the terms of the Montreal Protocol. One of the counterfeit refrigerant compositions that has drawn serious concern is methylchloride (R40) because of its flammability and deleterious interaction with the materials in refrigeration systems. There have been a number of reported accidents due to R40 being used as R134a or R134a contaminated by R40, resulting in HVAC or refrigeration system failures or serious human injuries. Specifically, the flammability of R40 can present unexpected risks for the operators maintaining refrigeration systems when improperly used as R134a. Moreover, many systems designed for use with R134a contain aluminum components, with which R40 can react to produce pyrophoric substance trimethyl aluminum that spontaneously ignites in air, creating a serious fire or explosion hazard. Other potential contaminants include R12 and R22 (chlorodifluoromethane). R152a (1,1-difluoroethane), although it does not contain chlorine, is also a contaminant of concern due to its flammability. Though contaminated refrigerants have been found in mobile air conditioners, stationary air conditioning systems and transport refrigeration systems in many countries, R40 has been identified to be the most detrimental. It is unknown what the lowest allowable concentration of R40 is in a refrigeration system without causing system failure; however, AHRI standard 700-2012, specifications of fluorocarbon refrigerants, would allow up to 0.5% of volatile impurities. Therefore, there is an urgent need of accurate detection technologies to identify R40 of low concentrations (as low as 0.5%) to prevent it from entering those systems. In view of the above, it would be desirable to have the capability to quantify contaminants, particularly R40, in refrigerants such as R134a.
Various types of sensors have been proposed for detecting contaminants in refrigerants. These include gas chromatograph/mass spectrophotometers (GC/MS), infrared analyzers, halide torching testers, etc. However, many such sensors have limitations that can impact their effectiveness. For example, GC/MS is highly accurate, but is expensive and not readily portable, rendering it unsuitable for deployment in the field for use with refrigerant systems. Portable infrared detectors have shown a detection limit in ca. 3% that is inadequate for preventing lower concentration R40 to be identified. Current IR detectors not specifically designed to address R40 can also produce false positive outcome. Halide torch testing can distinguish between chlorinated species and non-chlorinated species with extremely high sensitivity ca. 300 ppm; however, it is prone to false alarm because of the ultra-sensitivity and incapable of discern R40 from other relatively benign chlorinated contaminants.
In view of the above, there remains a need for new detection alternatives that may provide sensitivity to low contaminant levels and a robust response to eliminate false alarms, and be properly designed to make affordable detectors available for field deployment particularly mobile air conditioners and transport refrigeration systems.